Organic semiconductor devices manufactured in this way are known, an example being described in patent specification WO 01/20691. In such devices, the conductive polymer from which the electrodes are formed, serves as a highly efficient injector of electrons into the semiconductor. However, the conductive polymer is unfortunately not a very good electrical conductor. This introduces undesirable inefficiencies in the supply of current to and from the semiconductor. Worse still, the conductivity can deteriorate with time.